It is well known that oil is extracted from the ground by drilling a hole and installing a steel casing into the hole. Oil well holes may be several thousand feet deep and specialized pumps, known as Progressing Cavity pumps, are required to generate the high pressures necessary to pump the oil to the surface. The pumps are located at the bottom of the hole and driven by a drive string typically comprised of sucker rods which are connected together in end-to-end relation. Large electric motors and vertical drive heads are the preferred mode of driving the drive string.
In the current state of the art, manufacturers sell right angle drives as well as vertical drives. In a vertical drive, the input torque is parallel to the vertical axis of rotation of the drive string. In a right angle drive, the input torque is horizontal and perpendicular to the axis of the drive string and, therefore, gearing is required to convert horizontal torque to vertical torque. Both drives typically include a backspin speed reduction brake and thrust bearing arrangement.
Electrical power is frequently not available when an oil well is first put into service and, therefore, it is not possible to use an electric motor at the outset. Accordingly, it is customary to use a skid mounted gas engine to drive the pump. This requires the installation of a right angle drive head on the wellhead frame. When electrical power becomes available, the gas engine is replaced by an electric motor with a right angle motor mounting system in order to connect to the original right angle drive mechanism. The original right angle drive is retained to avoid purchasing a replacement vertical drive.
The problem with this approach is that right angle drives are more expensive and break down more frequently than vertical drives resulting in a loss of production. Furthermore, typical right angle drive heads are supplied with speed reduction ranging between 2:1 and 5:1 and these drives are not capable of the same high speed range as vertical drive heads. For example, a typical 2:1 right angle drive is rated at 400 rpm. Initially, the speed requirement is relatively low and there is no problem. When electrical power becomes available, the gas engine is replaced by an electric motor. As the well matures, water breaks through the oil and the pump speed must be increased to as much as 500 rpm in order to maintain the same oil production while pumping large volumes of water. Under these conditions, the original 2:1 drive is required to operate above its 400 rpm rating. This causes excessive lubrication oil temperatures, noise and premature wear, all leading to early drive head failures. While this is clearly an undesirable situation, no effective alternative has thusfar been proposed.